This invention relates to the fabrication of tank cars for railway use and, more particularly, to an underbody or underframe construction for such a tank car and a method of underframe construction.
During fabrication of the underframe assembly for a railway tank car, a critical step involves the attachment of the sill assembly portion of the underframe to the tank. A railway tank car underbody and a method of its construction are shown, for example, in U.S. Pat. No. 5,159,882, which is assigned to the same assignee as the present application. As shown in the center sill assembly 102 of FIG. 11 in the '882 patent, respective metal bars 128, 130 are welded to the respective upper, inner faces of side plates 118, 120. A top plate 132 is welded to the bars and extends longitudinally of the side plates. The cradle pad 108 for tank car body 106 is the welded to the center sill assembly.
The initial outboard weld; i.e., the weld between the cradle pad and the center sill assembly, is critical. In this regard, the construction shown in the '882 patent includes a weld attachment for assembly of the cradle pad 108 to the center sill assembly. This arrangement includes a bevel and a fillet weld. While this assembly method effectively attaches the cradle pad and center sill assembly together, the weld effectiveness is only as strong as the sill web. It will be appreciated that the length of the weld, and the amount of weld material which can be used to complete the weld is limited by the space limitations imposed by the design and fabrication of the center sill assembly. The problem with this current arrangement is that as haulers are looking for tank cars with higher load capabilities, the strength limitation imposed by this construction could inhibit the manufacture of tank cars with the desired increased capabilities.
Different approaches have been considered to provide a stronger weld between the cradle pad and center sill. One approach, for example, would be for the top cover plate to have a contoured upper surface. The contour would correspond to that of the botton portion of the cover pad attached to the center sill by welding along the top plate. While feasible, this approach is also expensive since the top plate would not be a standard piece of steel. In addition, the top plate would probably be heavier, thus adding weight to the railcar.